Motor driver free spin and user input

General discussion of using Roboclaw motor controllers
bisaac
Posts: 3
Joined: Wed May 30, 2018 5:39 pm

Motor driver free spin and user input

Postby bisaac » Wed May 30, 2018 5:54 pm

I am trying to use the roboclaw7a with a motor with hall effect encoders in an application which requires that I am able to have a user spin the motor when stopped as well as the roboclaw set a position with acceleration/deceleration.

When I power on the roboclaw 7A, my motors are easily spun by hand. As soon as drive the motors activated with any of the provided methods PWM, velocity, or position and back to zero velocity, the motors become more difficult to spin by hand. This tells me that the even when the motor is stopped, the back emf is being shorted across the driver.

My question: Is it possible to set the drivers back to this inactive state as it was when the board was powered to allow the user to change the motor position without the back emf going into the driver.

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Basicmicro Support
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Joined: Thu Feb 26, 2015 9:45 pm

Re: Motor driver free spin and user input

Postby Basicmicro Support » Thu May 31, 2018 10:38 am

There is no command to freewheel the motors but you can trick the Roboclaw into doing it by setting the Min Main Battery voltage higher than the current battery voltage. Then set it back to normal once your user is done doing whatever you need them to do. The reason this happens is the Roboclaw is setup to freewheel the motors if main voltage drops below minimum main voltage to help prevent brownouts.

bisaac
Posts: 3
Joined: Wed May 30, 2018 5:39 pm

Re: Motor driver free spin and user input

Postby bisaac » Thu May 31, 2018 12:36 pm

Thanks for a quick reply,

I tried this solution using IonStudio but It did not work.
Here are the steps I followed:

Power on board with 12v input power
motor is in freewheel.

Run pwm to 100%, then back to 0%
Motors are not in freewheel mode.

start conditions:
Max Main Battery 34v
Min Main Battery is 11v

Raise Min Main Battery Voltage to 20v
I get a MBLO yellow light.
Motors are not in freewheel mode.

Also tried with to raise Min Main Battery Voltage to 50v with same results.

Reading a post "Questions about regenerative braking"
"resistive braking (when you short the motor leads together(all energy is disipated as heat in the mosfets and motor windings)."

This seems to be the state the mosfets are in but I need them to be open, not shorted.

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Basicmicro Support
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Re: Motor driver free spin and user input

Postby Basicmicro Support » Fri Jun 01, 2018 10:18 am

Ah. I believe you may have to have a non 0 PWM for this to work. Please try that and let me know.

bisaac
Posts: 3
Joined: Wed May 30, 2018 5:39 pm

Re: Motor driver free spin and user input

Postby bisaac » Mon Jun 04, 2018 1:06 pm

If I understand what you are asking me to try, this did not work.
Here are the steps I followed:

Power on board with 12v input power
motor is in freewheel.

Run pwm to 100%, leave it there

Go to setting page and raise Min Main Battery Voltage to 50v.
Motor stops but not in free wheel mode but in break mode.

Just to clarify how I am determining if in free wheel mode, I can spin my geared motor and it will coast and slow down in about 1-2 seconds, consistent with not having the motor plugged in to the roboclaw. If the break mode is engaged, the spun motor will feel much harder to spin and will stop almost immediately.

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Basicmicro Support
Posts: 965
Joined: Thu Feb 26, 2015 9:45 pm

Re: Motor driver free spin and user input

Postby Basicmicro Support » Tue Jun 05, 2018 9:46 am

Email support for the pre-release version of Ion Studio. this has new firmware which should let you do what I described.


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